Sample implementation of Autocorrelation using Web Audio

autocorrelation.js

var findFundamentalFreq = function(buffer, sampleRate) {
	// We use Autocorrelation to find the fundamental frequency.
	
	// In order to correlate the signal with itself (hence the name of the algorithm), we will check two points 'k' frames away. 
	// The autocorrelation index will be the average of these products. At the same time, we normalize the values.
	// Source: http://www.phy.mty.edu/~suits/autocorrelation.html
	// Assuming the sample rate is 48000Hz, a 'k' equal to 1000 would correspond to a 48Hz signal (48000/1000 = 48), 
	// while a 'k' equal to 8 would correspond to a 6000Hz one, which is enough to cover most (if not all) 
	// the notes we have in the notes.json file.
	var n = 1024, bestR = 0, bestK = -1;
	for(var k = 8; k <= 1000; k++){
		var sum = 0;
		
		for(var i = 0; i < n; i++){
			sum += ((buffer[i] - 128) / 128) * ((buffer[i + k] - 128) / 128);
		}
		
		var r = sum / (n + k);

		if(r > bestR){
			bestR = r;
			bestK = k;
		}

		if(r > 0.9) {
			// Let's assume that this is good enough and stop right here
			break;
		}
	}
	
	if(bestR > 0.0025) {
		// The period (in frames) of the fundamental frequency is 'bestK'. Getting the frequency from there is trivial.
		var fundamentalFreq = sampleRate / bestK;
		return fundamentalFreq;
	}
	else {
		// We haven't found a good correlation
		return -1;
	}
};

var frameId;
var detectPitch = function () {
	var buffer = new Uint8Array(analyserAudioNode.fftSize);
	// See initializations in the AudioContent and AnalyserNode sections of the demo.
	analyserAudioNode.getByteTimeDomainData(buffer); 
	var fundalmentalFreq = findFundamentalFreq(buffer, audioContext.sampleRate);

	if (fundalmentalFreq !== -1) {
		var note = findClosestNote(fundalmentalFreq, notesArray); // See the 'Finding the right note' section.
		var cents = findCentsOffPitch(fundalmentalFreq, note.frequency); // See the 'Calculating the cents off pitch' section.
		updateNote(note.note); // Function that updates the note on the page (see demo source code).
		updateCents(cents); // Function that updates the cents on the page and the gauge control (see demo source code).
	}
	else {
		updateNote('--');
		updateCents(-50);
	}

	frameId = window.requestAnimationFrame(detectPitch);
};

You add the result n-times... Then shouldn't it be var r = sum / n; instead of var r = sum / (n + k);?
I want to understand it.

And I think I found a typo: fundalmental.

+P.S.: Exactly, the values have to be subtracted 127.5 and be divided by 127.5.

Works incorrectly on low frequencies (shows 6000), from 140 Hz to 370 Hz. Where is the mistake?